In a conventional fuel property detector shown in JP-5-133886A, a light-emitting diode (LED) emits light to fuel and a photodiode receives the light transmitted the fuel. Based on the transmitted light intensity, the detector detects concentration of ethanol contained in the fuel such as gasoline. Receiving the heat, temperature of the fuel may be increased and pressure in the fuel may fluctuate. Thereby, bubbles may arise in the fuel flowing in the fuel pipe. When the bubbles flows into the measure passage and adhere on at least one of a light emitting surface and a light receiving surface of the light-sensitive element, the light is refracted at the interface between the bubbles and the fuel. The intensity of the light entering the receiving surface of the light-sensitive element is fluctuated, so that an accuracy of fuel property detection may be deteriorated.
The present invention is made in view of the above matters, and it is an object of the present invention to provide a fuel property detector in which the fuel with bubbles is restricted from flowing into the measure passage, or the bubbles hardly adhere to the inner surface of the measure passage even if the fuel with bubbles flows into the measure passage. The fuel property is accurately detected according to the present invention.
According to the present invention, the fuel property detector is provided in a fuel pipe for detecting a property of fuel flowing through the fuel pipe. The fuel property sensor includes a housing having connecting ends which are connected to the fuel pipe, a measure passage which is defined in the housing and is opened at the connecting ends in order that the fuel flows therethrough, a light emitting element which is provided in the housing in such a manner as to emit a light toward the fuel in the measure passage, a light receiving element which is provided in the housing in such a manner as to receive the light passed through the measure passage, and a bypass passage which is defined in the housing in such a manner that the fuel flows therethrough. When the housing is connected to the fuel pipe, the bypass passage is located above the measure passage in a perpendicular direction in a cross section of the housing perpendicular to the measure passage. An inlet of the bypass passage is located above the inlet of the measure passage.
Receiving the heat, temperature of the fuel may be increased and pressure in the fuel may fluctuate, so that bubbles may arise in the fuel flowing in the fuel pipe. Since specific gravity of bubbles is lower than that of the fuel, the bubbles flows in an upper region in the fuel pipe. The fuel with bubbles flows into the bypass passage and the fuel without bubbles flows into the measure passage. Hence, the bubbles hardly adhere on a surface of the measure passage. Especially, the bubbles hardly adhere an emitting surface of light emitting element and a receiving surface of light receiving element. It is prevented from deteriorating an accuracy of fuel property detection may be deteriorated. The fuel property sensor can detect the fuel property with high accuracy.